Re: [Feature Request] git blame showing only revisions from git rev-list --first-parent

From: Jeff King <peff@peff.net>
Date: Sep 13, 2015, 10:07 UTC
Message-ID: <20150913100728.GA26562@sigill.intra.peff.net>
In-Reply-To: <xmqqy4gcxcp4.fsf@gitster.mtv.corp.google.com>

On Sat, Sep 12, 2015 at 01:29:43AM -0700, Junio C Hamano wrote:

Show 14 quoted lines

> >> -		for (p = commit->parents; p; p = p->next)
> >> +		for (p = commit->parents;
> >> +		     p && !revs->first_parent_only;
> >> +		     p = p->next)
> >>  			add_child(revs, p->item, commit);
> >>  	}
> >>  }
> 
> ... this is a total crap and shows that I am doubly an idiot.
> 
> The loop is a no-op when first-parent-only (the intent is to call
> add-child for just the first parent), so the code is stupid and
> wrong in the first place, but more importantly, the logic is utterly
> confused.

Whoops, yeah. I think you need "if (revs->first_parent_only) break;".

Show 5 quoted lines

> The thing is, traversing first-parent chain in reverse fundamentally
> is undefined.  You can fork multiple topics at the tip of 'master'
> and each of the topics may be single strand of pearls, but which one
> of the topics is the first-child-chain---there is no answer to that
> question.

In general I think I agree, but in the case of blame, we know that we are starting from a single tip (and we know because we are using first-parent that we remain in a single strand of pearls, because we follow only one parent and there are no cycles).

That is assuming that we create the set of children by traversing the first-parent history, though, which I am not at all sure about.

-Peff